Plastic containers are versatile for daily use as containers for beverages or food, due to their lightness in weight, economic efficiency, or excellent properties or adaptability to environmental problems. Especially, containers molded from polyethylene terephthalate (PET) are highly-demanded for containers for drinking water or soft drinks due to their excellent mechanical properties or transparency, and recently, they are quite regularly used by consumers as potable small containers and further as containers for hot drinks.
Synthetic resin containers as represented by polyethylene terephthalate (PET), which are very important as containers for drinking water and food in daily life, as stated above, are efficiently manufactured by stretch blow molding (sometimes referred simply to as stretch molding or blow molding) usually, wherein fluid are injected into preforms (pre-molded bottomed cylindrical molding materials) in molding dies, and then inflated and molded.
Conventionally, molding of preforms as molding materials of plastic containers and manufacture of containers were conducted mainly by molding preforms to multi-cavity molds by injection molding and then by performing stretch-blow molding to make container product. However, in this method, as the temperature of preforms were once cooled down or reduced to around room temperature, and the whole or body part of the preform were reheated afterwards before performing stretch blow molding, there are still problems including significant loss of heat energy for reheating, or cost burden of reheating facilities. Recently, technical demands for manufacturing economically excellent containers with higher performance and for increasing production efficiency have increased; therefore, development of better manufacturing methods or manufacturing devices are awaited in order to reduce the price of molding devices, increase production efficiency, or transit to low-temperature molding, etc.
As one solution, an injection stretch-blow molding, performing blow molding without reheating the preform immediately after injection molding (see for example, Japanese Laid-Open Patent Application No. 52-82967 (claim 1 and lower right column of page 1)) has been developed, while higher productivity cannot be realized as the consistency of time between the duration for injection molding and stretching blow molding is not good. Further, a method comprising the steps of molding a plurality of preforms at once by multi-cavity molds with an injection molding machine, and then performing stretch-blow molding immediately thereafter has been also developed. However, there are still problems including that container product with a constant level of quality are hardly obtained, as it is difficult to avoid transformation of performance caused by the temperature variation of the preform in the heat history difference, due to the time lag while waiting the molding order of the stretching blow molding machine; or by the variation in the stretching blow molding due to a thermal difference between the surface and the inner part of the preform, resulting from the thickness thereof.
Thus, in order to solve these technical problems of injection stretch-blow molding, a large number of proposition for amelioration has been disclosed so far, and the following improved methods can be exemplified: a method for reducing the injection molding cycle time, and improving operation ratio of a blow cavity, wherein the preform is cooled down, transported by a system continued from a transporting station to a molding station, and heated to perform stretch-blow molding (see Japanese Laid-Open Patent Application No: 11-165347 (Abstract)); and a method for improving credibility and speed of molding by providing a cooling station and a heating station for preforms, and converting the transporting pitch between the preforms to a stretch blow molding pitch (see Japanese Laid-Open Patent Application No. 2002-337216 (Abstract)).
On the other hand, a compression molding machine has been proposed as a molding device which is less expensive than an injection molding device, which could be downsized, and which enables molding at a low temperature, and a rotary compression molding machine (a rotary-and movable type compression molding machine) (see Japanese Laid-Open Patent Application No. 60-245517 (claim 1)) wherein a plurality of molding dies are mounted on a rotating disk has been developed and applied, in order to enhance their mass productivity to improve their production efficiency. Further, a molding method supplying materials by extrusion and using the rotary type-compression molding machine (see Japanese Laid-Open Patent Application No. 2000-25729 (claim 1 and FIG. 1)) has been developed as a method for molding preforms by using rotary-type compression molding machines. Production efficiency has improved dramatically by applying the rotary-type molding machine, and recently, the molding method by extrusion compression molding appears to be the most promising method for manufacturing preforms.
As stated above, in the injection stretch blow molding of plastic containers, even by manufacturing a large amount of preforms with a multi-cavity molds by injection molding method, there are still problems including that container product with a constant level of quality are hardly obtained, resulting from the transformation of performance caused by the temperature variation of the preform up to stretch blow molding; or by the variation in the stretching blow molding due to a thermal difference between the surface and the inner part of the preform, resulting from the thickness thereof. In order to solve these technical problems, a large number of proposition for amelioration has been disclosed so far, while it is hard to say that problems including transformation of performance caused by the temperature variation of the preform in the heat history difference, or the variation in the stretching blow molding due to a thermal difference between the surface and the inner part of the preform, resulting from the thickness thereof have been resolved sufficiently.
On the other hand, in a compression molding machine which is less expensive than an injection molding device, which could be downsized, and which enables molding at a low temperature, a rotary compression molding machine for preforms wherein a plurality of molding dies are mounted on a rotating disk has been developed and good results for economic efficiency and production efficiency were obtained. However, even a method for manufacturing consecutively containers by combining stretch blow molding with compression molding to further improve molding methods has been conceived, the method has not been disclosed at all.
Moreover, by applying a new method for manufacturing containers which combines compression molding with stretch blow molding, to make a system continued from compression molding to stretch blow molding, the reheating device for preforms to be used before stretch blowing would be unnecessary, and thus generating an economic effect as the energy necessary for heating preforms would be omitted. Further, as the compression molding machine and the stretch blow molding machine are independent each other, higher productivity having excellent consistency in molding speed can be realized by setting independently the number of molding dies according to the molding speed. However, in contrast of these merits, there are still problems that are not resolved, including that container product with a constant level of quality are hardly obtained, as it is difficult to avoid transformation of performance caused by the temperature variation of the preform; or by the variation in the stretching blow molding due to a thermal difference between the surface and the inner part of the preform, resulting from the thickness thereof.
In the light of the above condition in the technology of manufacturing synthetic resin containers by stretch blow molding, in order to industrialize a new molding method wherein compression molding is combined continuously with stretch blow molding, which is an excellent method from the view of economic efficiency or production efficiency, the object which the present invention targets is, to manufacture with high producibility container product with a constant level of quality, by this new molding method, by resolving problems including transformation of performance caused by the temperature variation of the preform; or by the variation in the stretching blow molding due to a thermal difference between the surface and the inner part of the preform, resulting from the thickness thereof, in the molding method.